The word-frequency file contain words in the target language with their associated frequency in a corpus. Entries in this file are used to calculate the keystrokes-per-character measurement and the words-per-minute performance prediction.
The words-per-minute prediction is based on a Fitts' Law model to calculate movement time between key. Slope and intercept values represent coefficients in Fitts' Law. The tmin value represents the time to repeat the last key press.
The presence of ambiguous words requires the user to expend perceptual and cognitive effort when using ambiguous keypads. The Model Human Processor (MHP) by Card, Moran and Newell models human mental processes and presents timing values representing the duration of mental operations. By incorporating such timing values into the equation for movement time, the WPM performance prediction is adjusted to account for this effort. The following is a description of each component: